Thermionic tube



Dec. 27, 1932. F. s. MCCULLOUGH 1,392,066

THERMIO NIC TUBE Filed Nov. 20, 1926 INVENTOR fl x/74% Q fZQ/M Patented Dec. 27, 1932 PATENT OFFICE FREDERICK S. MCCULLOUGH, F EDGEVOOD, PENNSYLVANIA THERMIONIC TUBE Application filed November 20, 1926.

This invention relates to thermionic tubes, and more particularly the tubes of the socalled three electrode type.

Electron tubes of the three-element type have heretofore been made in two different ways. According to one common form of construction, there is a filament and a plate at one side of the filament, and there is a grid interposed between the filament and the plate. 19 In the second, and more commonly used type of tube, the grid entirely surrounds the filament, and the plate in turn entirely surrounds the grid. The second design is considered the more efficient. In the second design, however, the tube has a relatively high internal capacity, due to the relatively large surfaces of the grid and the plate. This high internal capacity is objectionable in many types of circuits, because it permits of the pas- 0 sage of high frequency oscillations from the grid to the plate without amplification thereof, and because it has a greater tendency toward self-oscillation.

The object of the present invention is to provide a tube having a low internal capacity as compared with standard tubes, but which will have practically the same mutual conductance, amplification constant, and plate current as the standard tube, which has the grid entirely surrounding the filament and wherein the plate entirely surrounds the grid.

The invention may be readily understood by reference to the accompanying drawing which illustrates certain embodiments of my invention, and in which Figure 1 is a more or less diagrammatic view presenting a vertical section through a tube embodying my invention, certain parts of the several electrodes being broken away for more comolete illustration thereof.

Figure 2 is a vertical section in a plane at right angles to the section of Fig 1.

Fi ure 3 is a transverse horizontal section in the plane of Line IIIIII of Figure 1.

Figure i is a View similar to Figure 3 showing a slightly modified construction.

In the drawing, 2 designates the base of the tube. This may be a base of any standard, or preferred construction, and mounted in the base is the glass envelope 3 of the tube. The

Serial No. 149,596.

tube has the usual stem 3'', having filament lead wires 4 and 5 and passing therethrough. Connected to the lead wires 4: and 5 are the opposite ends of the filament 6. At each side of the lead wires 4 and 5 are wires 7 and 8 which support posts 9 on which the grid 10 is supported. The grid is preferably in the form of a fine wire wound about the posts 9 in the usual manner, the filament being entirely surrounded by the grid. Supported on a central post 11, secured in the stem of the tube, is the plate 12. The plate extends up along one face of the grid out of contact therewith, so that one side of the grid structure is disposed between the filament and the plate, while the other side of the grid structure is remote from the plate and on the opposite side of the filament therefrom.

According to the present invention, there is preferably provided a metal shield 13 on the side of the grid opposite the plate. This shield 13, which I term an electron collector, or reflector, is preferably Wider than the plate and has the side edges thereof turned inwardly so as to partly enclose the grid, as clearly shown in Figure 3. It is carried on vertical posts 1d at the opposite edges thereof, and these posts are secured to the ends of curved supporting wires 15 in the stem of the tube.

In the base of the tube are the usual contact pins, of which there are four. These pins are arranged in the standard fashion. One of the pins, 16, is connected to one of the wires, 7, which carries the grid. Another pin, 17, is connected to the central post 11, which supports the plate. The other two pins, 18 and 19, are connected to the lead wires 4 and 5 so as to connect with opposite ends of the filament. In order that the shield, or collector 13. may be of the same potential as the filament, and therefore not draw any considerable electron current to itself, or accumulate any charge. it is preferably connected to one of the filament posts, such as the post 19, as illustrated through wire 20.

For supporting the topof the filament, there isprovided a hooked wire 21 carried on a support 22, which has an insulator 23 thereon so as to prevent the passage of curby excessive radiation.

rent from the shield to the filament through the support, the support 22 being carried on one of the posts 14:.

From the foregoing it will be seen that the plate is on one side of the grid and filament only, while the grid entirely surrounds the filament. As compared with a standard tube having a grid of substantially the same dimensions, the plate of the present tube is only about one-third the area of the plate of the standard tube, so that the tube has a consequently much lower internal capacity by reason of the coupling between the grid and the plate. At the same time,. the tube has the same electrical tuning characteristics as the standard tube. In other words, the tube has the same electrical characteristics between the filament and the grid, as compared with a standard tube, but is out of balance as compared with the standard tube, as the standard tube has the plate completely surrounding the grid. It has been found that tubes embodying the present invention will have practically the same mutual conductance as standard tubes, the same amplification constant, and the same plate current under the same operating conditions.

It has been found that the grid collects the electron flow from the filament on all sides of the filament and transfers it to the plate which is at one side of the filament only. The tube is, therefore, different from the first type of tube herein mentioned wherein there is a grid interposed between a plate on one side of the filament and the filament. By entirely surrounding the filament with the grid instead of simply having a grid on one side of the filament extending up between a plate and the filament, it is possible to keep the operating characteristics of the tube substantially similar to those of the standard tube.

Theshield, or collector 13, enclosing the grid on the side opposite the plate, serves to prevent any slight loss of the electron flow from the filament away from the plate electrode, and to confine the electron flow to the space immediately around the filament and grid. It also serves to prevent loss of'heat x Since the grid surrounds the cathode while the anode is located only on one side thereof, the grid may define an area more than twice that defined by the anode, as will be clearly apparent from an inspection of'Figure 3. Moreover. the shield 13. which is located entirely outside the space between the grid andthe plate, defines an area greater thanthe area of the anode. Both of these relations are desirable.

- In the arrangement shown in Figure 4, the construction of the electrodes is slightly modified, but the same general principle is followed. In this figure, 25 designates filament wires, each of which is surrounded by a grid 26. The plate electrode, or anode, has a central web portion 27 with end portions 28 directed toward the respective filaments. Outside the grids 26, and opposite the plate surfaces 28, are shields 29 corresponding in function to the shields 13 described in connection with the structure shown in Figure 1.

This embodiment of the invention merely illustrates howthe invention may be adapted to tubes wherein separate grids and separate filaments are employed. The operation of the invention is the same as that shown in connection with Figure '1.

' The tube embodying the present invention is applicable to any circuit wherein a standard tube is employed, the use of the tube being diagrammatically illustrated in my copending application, Serial No. 145,7 75, filed November 2, 1926.

WVhile I have illustrated and described certain specific embodiments of my invention, it will be understood that the invention is not restricted to the specific constructions shown, but that it may be otherwise embodied, and that various changes and modifications may be made therein within the contemplation of the following claims.

I claim 1. An electron tube having a cathode, a grid surrounding the cathode, an anode outside of the grid on one side of the grid and cathode only, and a conducting shield enclosing the other side of the grid and cathode, said shield being connected with the cathode.

'2. An electron tube having a cathode, a grid surrounding the cathode, an anode outside the grid on one side of the cathode only, the area. defined by the grid being at least twice the area of the anode, and a conducting shield connected with the cathode and embracing that portion of the grid which is not disposed between the cathode and the anode.

3. An electric discharge tube containing a thermionic cathode, a grid, an anode spaced from the grid, a shielding element outside the grid and parallel with the anode and located entirely outside the space between thegrid and the anode, an evacuated vessel in which the electrode elements are contained, a press in which supporting wires for some of the electrodes are carried, said shielding'electrode having two supporting wires in the press, and an insulator carried on the shielding electrodein which is a support for another of the electrodes within the vessel.

In testimony whereof I have hereunto set my hand. Y FREDERICK S. MGCULLOUGH. 

